TM-851 0429.000

Fermilab,

ACCELERATOR DIVISION CAPACITOR STORED ENERGY DEVICES

J. Ryk

February 13, 1979

An attempt has been made to list all devices in the Accelerator

Division that use energy storage capacitors. Safety requirements

as stated by the National Electrical Code (NEC) are considered and

recommendations for safe practices are listed.

1. Code Requirements, NEC 1978, Article 460

1.1 Capacitors containing more than 3 gallons of flammable

liquid are to be stored in vaults or outdoor fenced

enclosures.

1.2 Capacitors are to be enclosed, located or guarded so

that accidental contact is not possible, unless the area

is only accessible to authorized and qualified persons.

1.3 Isolating means are required for capacitors that will be

removed from service. The isolation measure is to provide

a visible gap in the electrical circuit.

1.4

1.5

Overcurrent protection is required to detect and interrupt

fault current that is likely to cause dangerous pressure

within an individual capacitor.

Identification is required. Nameplate information to

include: manufacturer frequency KVAR or amperes number of phases amount of liquid flammable or non-flammable

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1.6 A means of discharge is required to reduce the residual

voltage to 50 volts or less:

within 5 minutes if initial voltage is over 600 volts

within 1 minute if initial voltage is less than 600 volts

2. Discharging Capacitor

The stored energy in a capacitor is W = %CV2=$QV with

C in farads

V in volts

Q in coulombs

W in Joules (Wattsec)

When a capacitor, initially charged to a voltage V,, is discharged

through a resistance R, the discharge current at first instance is

v, = -V,/R. Thereafter the current varies according to i = i. E -t/RC .

The charge on the capacitor decreases during discharge according to

q = QoE-t/RC, where Q. is the initial charge. The National Electric

Code states that the residual voltage is to be reduced to 50 volts

within 1 minute for V, < 600 volts and within 5 minutes for V, > 600

volts. Since V = Q/c, the voltage at discharge follows the same curve

as the charge, or v = V,E -t/RC . From this we can find the resistance

necessary to meet the code requirement for discharge time.

= E-t/RC In v t -= --

vO RC

In v, = t V RC

R=ElnV 0

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with t = 60 set for V < 600 volts 0

t = 300 see for V. > 600 volts

vO = peak operating voltage

v = 50 volts

If a capacitor bank already has a discharge resistor connected,

we can find the discharge time from:

t = RC In '0 v

All capacitor banks in the Accelerator Division have been listed

with their voltage, capacitance and stored energy. Values of dis-

charge resistance required per NEC are listed together with the dis-

charge times.

Warnings

1. In order to meet the NEC requirement for overcurrent protection

it is customary practice to use fuses to protect either individual

capacitor cases or complete capacitor banks. If a fuse blows

and the capacitor has internal discharge resistors, the

2.

capacitor will automatically discharge. If a fuse blows and

the capacitor has no internal discharge resistor, which is very

often the case, the capacitor will stay charged.

If a blown fuse is detected, always discharge the capacitor,

short it and ground it.

In general a capacitor does not return, on discharge, the full

amount of energy put into it. Some time after the discharge an

additional discharge may be obtained. This phenomenon is known

as dielectric absorption. Before working on a device with

capacitors, first discharge it, leave the discharge device on it,

short and ground the capacitors, Leave the capacitor shorted

and grounded during the complete servicing time.

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3. When storing and transporting capacitors, always have the

capacitors shorted.

4. An impulse discharge of % Joule causes muscular contraction.

An impulse discharge of 50 Joule is lethal (ref. 1).

5. If no good contact is made with the discharging device, it is

possible to create welding of the discharge device to the

stored energy device. See Appendix A.

6. Some capacitors are located in radiation areas, so radiation

rules need to be observed in addition to all other safety rules.

7. Many capacitors use askarel as the liquid dielectric. The

principal constituent of askarel is PCB (polychlorinated

biphenyl) a toxic substance with adverse ecological effects.

These capacitors should be marked with a sticker, indicating

that they contain PCB.

When a PCB filled capacitor fails, it has to be disposed of in

accordance with PCB disposal requirements.

8. Whenever a system has been subjected to a hi-pot test, it should

be treated as a charged capacitor. Proper discharge techniques

are to be followed prior to working on the system, see also

Appendix B.

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SAFETY

Capacitors are a potential shock hazard, explosion hazard,

fire hazard and toxicity (PCB) hazard.

Shock Hazard

1. Before working on capacitors, always remove power from the

capacitors by a visible disconnect.

2. After disconnecting the power, the capacitors still present a

potential shock hazard due to the fact that a charge may still

be existing. The capacitors should be discharged prior to

handling.

Some systems have a mechanical automatic discharge system.

Some capacitors have internal discharge resistors.

Under no condition shall these discharge devices be considered

as adequate. As stated by NEMA Publication No. CP-1-1976, "The

use of a discharge device is intended to supplement rather than

to displace the short-circuiting of a capacitor unit before

handling".

3. After disconnecting the capacitor from the power source, wait

at least 5 minutes, then short and ground the capacitor equip-

ment and individual capacitors, using an insulated ground stick.

Shorting should be terminal to terminal and terminal to case.

Individual units should also be shorted because shorting of a

complete capacitor bank is ineffective in case of a fuse opera-

tion or other disconnection of an individual capacitor unit.

4. Ground sticks should have a discharge resistor so that initial

discharge of the capacitors is through a resistor (see attached

SKMS81375). The discharge resistance as required by the National

Electric Code requirements is listed for the different equipments.

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5.

6.

7.

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Westinghouse, for their Wemcol impregnated capacitors (ref. 4)

suggests using a resistance in ohms about equal to the maximum

peak voltage that may have been on the capacitor. The resistor

should have a peak voltage capability greater than the maximum

peak voltage on the capacitor and an energy capability greater

than the energy stored in the capacitors.

After discharging the capacitors, a shorting connection should

be installed between the terminals and a ground connection should

be left on till all work on the equipment is completed.

If an insulated wire is used from ground stick to ground, it

should have clear insulation, so that wire continuity is visible.

Ground sticks should always be kept clean!

Explosion Hazard

Capacitors, fused or unfused, may rupture upon failure. They

may explode also during hi-pot tests; it is therefore important that

the capacitors are installed or shielded in such a way that personnel

are protected from exploding capacitors.

Sometimes capacitors show bulging due to internal pressure from

gassing. These capacitors should be disposed of. It is also recom:.

mended that the internal pressure be relieved before handling by

breaking off a bushing terminal with a long pole, or by puncturing

the case with a punch after covering the capacitor with a heavy cloth.

The puncture should be made where a minimum of fluid leakage will

occur. Provisions should be made to collect the drained fluid.

Avoid liquid contact with skin and eyes and avoid exposure to

fumes in an unventilated area.

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Fire Hazard

A fire

used in the

hazard exists where a flammable dielectric fluid is

capacitors. This should be stated on the nameplate.

The location of these type capacitors should be such that a possible

fire after capacitor failure and rupture can be contained in accord-

ance with the National Electric Code.

Conclusion

There are a large variety of devices with capacitive stored

energy in the Accelerator Division.

Many of the devices have automatic discharge equipment. There

are a variety of discharge and grounding sticks in use. The Safety

Department is in the process of procuring grounding sticks.

Due to the variety of the different systems, it is not possible

to treat each system alike. It is recommended that the persons

responsible for the different systems write their own safety discharge

and grounding procedures based upon the general recommendations as

listed in these guidelines. Several of the accelerator systems have

existing written procedures with pictorial guides. This would be a

good overall system, very valuable for training of new people.

JR/nep

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Appendix A

Welding of the grounding stick to the capacitor can occur

depending on capacitor energy. A large amount of stored energy should

be discharged using the proper discharge resistance and using positive

contact procedure. Intermittent contact will initiate welding.

The amount of energy needed to heat and weld 1 cc of copper

can be found as follows:

Copper: melting point = 1083 C

specific heat = .092 cal/g/oC at 20°C

Latent heat of fusion = 49 Cal/g

Density = .3223 lb/in3

The temperature rise to the melting temperature AT = 1083-20 = 1063°C.

To heat one gram of copper to melting temperature, it takes

. 092 x 1063 = 97.8 calories

To melt 1 gram of copper, takes 49 calories

To heat and melt 1 gram of copper it takes 146.8 calories.

One cubic inch of copper weighs .3223 pounds = .3223 x 453 = 146 grams 1 cm3 of weighs 146 copper

(2.54j3 = 8.9 grams.

To heat and melt 1 cm 3 of copper takes: 146.8 x 8.9 = 1308 calories.

1 Joule z .239 calories

In order to heat and melt 1 cc of copper, it will take - 1308 = 5473 . 239 joule:

A discharge of 5.5 kJ can cause melting of 1 cm' of copper, which would

mean welding of the grounding rod to the energy storage system. The

same calculations for steel show that 4.3 kJ is enough to heat and

weld 1 cc of steel.

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A typical weld with a spot diameter of .5 cm and a penetration of

one-fifth the spot diameter, corresponds to heating and melting of

. 040 cc. of metal.

The average cold resistance of a spot this size is .5 milliohm

(ref. 3).

This weld would be accomplished with an energy .04 x 5473 = 220 Joules.

If this energy is discharged in .l second, the average power would

be 2200 Joules per second or 2200 watts. From P = i2R = 'g we find

that the welding current will be G3 = 2080 amps at a voltage

of 1 volt across the weld.

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Appendix B

Capacitance of Cables

The capacitance of a one-conductor shielded cable is given

by the formula C = 7.35(SIC) log ;

where C = capacitance of the cable in picofarads per foot

SIC = dielectric constant of the insulation

D = diameter over the insulation

d = diameter under the insulation

typical values of SIC

polyvinyl chloride (PVC) 5.0 - 8.0

butyl and EP insulation 3.5

polyethylene insulation 2.3

cross-linked polyethylene 3.5 - 6.0

A typical example is our 13.8 KV feeder cable, 750 MCM with

cross-linked polyethylene insulation.

Typical length is % circumference of the main ring, or

10600 feet

D = 1.45"

d = 1.1"

c = 7.35 x 5 = 306 pf/ft

for 10,600 ft., C = 3.27nf

At the typical test voltage of 29 KVDC, the feeder has a stored

energy of 1362 Joules.

To discharge the feeder in accordance with the National Electric Code

to 50 volts in 5 minutes, requires a discharge resistor of 15 MQ.

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DEVICES WITH CAPACITIVE ENERGY STORAGE

MAIN RING

DEVICE

CAPACITANCE PEAK STORED NEC NEC C VOLTAGE ENERGY Required Required

V gv 2 Discharge Discharge Resistance Time t

IJf VOLTS JOULES KS2 Set REMARKS

RF Anode Supplies 45

RF UC 4 Modulators amp .1

Cap. Tree per phase 2940

C48 Kicker .080

B24 Pulsed Quad 240

E48 Pinger 240

C34 Pulsed Quad 240

A34 Pulser 240

F13 Pulsed Quad 240

RF Test Station 11

Harmonic Filter 25

Power Supplies Passive Filter 200

$I Power Supplies Active Filter 690000

A, Power

Supplies (2) 88800

34,000 26010 1022

480 .46 6631 30,000 45 470,000

12,000 212000 18.6

200 KV 400 493000

2000 480 340

2000 480 340

2000 480 340

2000 480 340

2000 480 340

35000 6700 4160

8000 800 2364

1000

40

150

100 500

552 60 ex. 50R disch. res.

999 60 60 ex. 3352 disch. res.

300

60 300

300

300

300

300

300

300

300

300

300

oil filled

300

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DEVICE

200 MeV Chopper

Sl and S2 Pulsed Power Supplies

Electrostatic Injection Infl ector

ORBUMP Supply H+

ORBUMP Supply H-

Hor & Vert Notch Power SUPPlY

Bex Back

GMPS Circuit Cap, Each Girder

GMPS Filters

East and West RF Anode Supplies

RF ac-

-12-

DEVICES WITH CAPACITIVE ENERGY STORAGE

CAPACITANCE C

uf

.17

PEAK STORED VOLTAGE ENERGY

V 1-,cv 2

VOLTS JOULES

1000000 850

NEC NEC Required Required Discharge Discharge Resistor R Time t

KS-2 Set

232000 300

1200 1.300 1014 76 300

.04 70000 98 1035000 300

2400 2250 6075 33 300

1100 3500 6738 64 400

.34 32000 174 137000 300

1660 350 102 19 60

8300 1000 4150 12

2800 1000 1400 36

45

4

34000 26010 1022

480 .46 6631 30000 45 470000

60000 135 564000 60000 270 282000

300

300

300

3:;

300 300

300

300 300

300

300

Modulators output- .l

MK 90 cable .075 internal .15

MP 01 Pulsed Septum 2400

MKS Ol/ cable .075 MKS-02 internal ..15

RF Test Station 11

MP-70 2400

BOOSTER

1500 2700 37

50000 94 579000 50000 198 289500

3500 6700 4160

1500 2700 37

REMARKS ex. 1000 KS2 disch. res.

ex. 75 KS2 disch. res.

ex 100 KS2 disch. res.

ex. 100 KR disch. res.

oil filled

oil filled

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DEVICES WITH CAPACITIVE.ENERGY STORAGE

SWITCHYARD

DEVICE

MK-120

CAPACITIVE PEAK STORED NEC Required NEC C VOLTAGE ENERGY Discharge Required

V J-;cv 2 Resistor Discharge (max) R

Ilf Time (max)

VOLTS JOULES K1;2 t (set) REMARKS

240 2000 480 340 300

MV-T90 inv 970 415 84 29 60

MVT-101 inv 970 415 84 29 60

MVT-120 inv 970 415 84 29 300

PVT-80 240 2000 480 339 300

PVT-91 240 2000 480 339 300

PVT-101 240 2000 480 339 300

PVT-103 240 2000 480 339 300

Pos. Pulse 480 2000 960 169 300

Ang. Pulse 480 2000 960 169 300

EXT 60800 400 4864 .475 60

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DEVICES WITH CAPACITIVE ENERGY STORAGE

LINAC

CAPACITANCE PEAK STORED NEC NEC C VOLTAGE ENERGY Required Required

V gv* Discharge Discharge Resistor Time

(max) hod DEVICE

PA bias SUPP’iY

220

VOLTS JOULES ‘KG iec REMARKS r\nrr ex. disch. resistor

Modulators plate- 100

4616 Anode driver 24 SUPPlY screen 40

7651 Anode Supply 40

Quad Cl-C4 2200 Supplies Cll-C22 240

2700 6500

800 2100

340 600

mu 140 KQ 300 ex. disch. res

200 KQ

Both Haeflies

HV PS Cap Bank

PFN Power Bank

PFN Turn-Off SUPPlY

Ion Pump Power Supply

Varian p.s. for ion pump

Triplet p.s.

Chopper U.V.

H- Extractor

Hf Extractor .048 12000 .24

HV p.s. (anode supply)

Arc modulator

Cup pulser

.005 750000 1406 6240MS2 300

30.8 52000 41640 1402 300 aut gnd 2.5m to Ofi

1000 600 180 24 60

20 2000 4066

2 5000 25 32600

.5 10000 25

360000 40 288

.27 30000 122

.a 30000 45

113MS1

we

174MR

469MR

1100MQ 300

8 8000 256

3900 300 176

900 600 162 27 1800 300 81 19

20000 4800 3500 245

3000 180

800 704 800 77

2086 1765

1832

4:;

300 aut gnd 1KR to OR 300 aut gnd 25Ks2

300 aut gnd 25KsZ

300 aut gnd 1OOQ 600 aut gnd 100R

300

300

300

60

300

300

300

300 300

ex. 10MM disch. res.

ex. 4R disch. res.

aut gnd 4000Mn to Or;2

ex. 27OKs2 disch res +2.5MR solenoid

ex. 333MR disch res safety ckt 1OMQ

ex. 3Om disch res

ex. 47Kr;2 disch res ex. 47m disch res

TM-851

REFERENCES

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1.

2.

3.

4.

5.

6.

7.

ZGS Safety Information - December 10, 1964.

National Electric Code - 1978.

Welding for Engineers, J. Wiley.

Westinghouse Publication I.L. 39-311-1A.

NEMA CP-1, 1976.

Ten Commandments of Electronic Safety.

Okonite Bulletin 721.1.

JR/nep

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W&inghouse Electric Corporation /GwuAL GEOUx/p/M~ t$5&Ge 0 w

TITLE

DIV & PLANT LOCATION- DAD--BLOOMINGTON. IND. U.S.A

ELECTR I C SHOCK, SEVERlTY FACTORS ~

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The severity of the shock received when a person becomes part of an electrical circuit is affected by three primary factors. These factors are:

(1) The rate of flow of current through the body, measured in milliamperes;

(2) The path of current through the body; and (3) The length of time the body is in the circuit.

Other factors which may affect the degree of shock are: the frequency of the current, phase of the heart cycle when shock occurs, and the physical and psychological condition of the person. The following are measurements of injury related to current for the case of 60 cycle, 120 volt alternating current.

Less than l/2 milliampere -- No sensation. l/2 to 2 -- Threshold of perception. 2to 10 -- Muscular cant raction

(mild to strong). 5 to 25 -- Painful shock, inability to

let go. Over 25 -- Violent muscular contraction. 50 to 100 -- Ventricular fibrillation. Over 100 -- Paralysis of breathing.

Direct Current Voltage 60 milliamperes -- Muscular contraction. 500 milliamperes -- Lethal.

Impulse Discharge l/4 joule -- Muscular contraction. 50 joule -- Lethal.

Over 100, 000 cycles there is no sensation to shock but strong possibility of burns.

In estimating possible body current, assume a 500 ohm body resistance between major extremities. This low figure might be attained when the skin is initially injured by shock from voltages as low as 50 Volts or from damp contact conditions.

Example: 50 Volts A. C. divided by body resistance of 500 ohms, equals 100 milliamperes, which is lethal if through body.

Ref: LOS Almos, Electrical Safety Guide; Safety In Industry, Bulletin No. 216

DATE December 16, 1964 PAGE 1 OF I